WorkStruct: Pass the work_struct pointer instead of context data

Pass the work_struct pointer to the work function rather than context data.
The work function can use container_of() to work out the data.

For the cases where the container of the work_struct may go away the moment the
pending bit is cleared, it is made possible to defer the release of the
structure by deferring the clearing of the pending bit.

To make this work, an extra flag is introduced into the management side of the
work_struct.  This governs auto-release of the structure upon execution.

Ordinarily, the work queue executor would release the work_struct for further
scheduling or deallocation by clearing the pending bit prior to jumping to the
work function.  This means that, unless the driver makes some guarantee itself
that the work_struct won't go away, the work function may not access anything
else in the work_struct or its container lest they be deallocated..  This is a
problem if the auxiliary data is taken away (as done by the last patch).

However, if the pending bit is *not* cleared before jumping to the work
function, then the work function *may* access the work_struct and its container
with no problems.  But then the work function must itself release the
work_struct by calling work_release().

In most cases, automatic release is fine, so this is the default.  Special
initiators exist for the non-auto-release case (ending in _NAR).


Signed-Off-By: David Howells <dhowells@redhat.com>

1 files changed, 8 insertions, 5 deletions

diff --git a/kernel/kthread.c b/kernel/kthread.c
index 4f9c60ef95e8..1db8c72d0d38 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -31,6 +31,8 @@ struct kthread_create_info
         /* Result passed back to kthread_create() from keventd. */
         struct task_struct *result;
         struct completion done;
+
+        struct work_struct work;
 };
 
 struct kthread_stop_info
@@ -111,9 +113,10 @@ static int kthread(void *_create)
 }
 
 /* We are keventd: create a thread. */
-static void keventd_create_kthread(void *_create)
+static void keventd_create_kthread(struct work_struct *work)
 {
-        struct kthread_create_info *create = _create;
+        struct kthread_create_info *create =
+                container_of(work, struct kthread_create_info, work);
         int pid;
 
         /* We want our own signal handler (we take no signals by default). */
@@ -154,20 +157,20 @@ struct task_struct *kthread_create(int (*threadfn)(void *data),
                                    ...)
 {
         struct kthread_create_info create;
-        DECLARE_WORK(work, keventd_create_kthread, &create);
 
         create.threadfn = threadfn;
         create.data = data;
         init_completion(&create.started);
         init_completion(&create.done);
+        INIT_WORK(&create.work, keventd_create_kthread);
 
         /*
          * The workqueue needs to start up first:
          */
         if (!helper_wq)
-                work.func(work.data);
+                create.work.func(&create.work);
         else {
-                queue_work(helper_wq, &work);
+                queue_work(helper_wq, &create.work);
                 wait_for_completion(&create.done);
         }
         if (!IS_ERR(create.result)) {